Organic solar cells (OSCs) becomes a really hot research topic for light in weight, high flexibility, large-area production, etc. Researchers are working to improve the performance and environment-friendly of OSCs. They proposed a series of strategies in improving PCE and stability such as synthesis new type acceptors, optimize battery process and introduction of electron transport layer.
Fig 1 Device structure of the OSCs
“Nowadays, developing solution-processed stable organic cathode interlayers (to replace the active metal cathode and enhance the device stability) is an important topic in the field of organic solar cells. A number of efficient organic cathode interlayers have already been reported, however they are generally very thickness-sensitive (usually less than 10 nm). The thickness-sensitive problem excludes their compatibility with large-area roll-to-roll processing technology, which is required for low-cost flexible organic solar cells. It is thus highly desirable to find thickness-insensitive organic cathode interlayers.”
Fig. 2 (a) Device structure of the PSCs. (b) Synthetic route towards PDI-interlayers. (c) Film absorption spectra of PDI-interlayers (105 cm-1). The inset shows the solution absorption. (d) Cyclic voltammograms of the PDIs.
Yongfang Li etc reported two perylene diimide (PDI) derivative cathode interlayers in 2014, differing only in the presence of either amino (PDIN) or amino N-oxide (PDINO) terminal substituent(Fig. 1b). In this paper, for the first time thickness-insensitive small-molecule-based cathode interlayers are reported. Notably, the two solution-processed cathode interlayers they designed and developed are easy-accessible using environmentally friendly reagents, and they exhibit promising performances in photovoltaic applications.
Fig 3 Device structure of the OSCs and H-bonding improves interlayer compatibility
In 2020, Zhiguo Zhang and Yongfang Li  etc. reported a hydrogen-bonding interfacial material, aliphatic amine-functionalized perylene-diimide (PDINN), which simultaneously down-shifts the work function of the air stable cathodes (silver and copper), and maintains good interfacial contact with the active layer. The OSCs based on PDINN engineered silver cathode demonstrate a high power conversion efficiency of 17.23% (certified value 16.77% by NREL) and high stability. The results indicate that PDINN is an effective cathode interfacial material and interlayer engineering via suitable intermolecular interactions is a feasible approach to improve device performance of OSCs.
 Energy Environ. Sci. 2014, 7, 1966-1973.
 Nat Commun. 2020, 11, 2726.